The invention relates to device for scanning a magneto-optical recording layer, comprising a radiation source and an objective system for forming a radiation beam focused to a scanning spot on the recording layer, and a magnet coil comprising a winding with a core arranged between the objective system and the recording layer for generating a magnetic field at the location of the scanning spot. The core of a coil is meant to be the central part of the coil inside the winding.
Magneto-optical record carriers can be written and read by means of such a device. There are two writing methods. In the first method there is a constant magnetic field at the location of the scanning spot, while the radiation intensity of this scanning spot is modulated, dependent on the information to be recorded. In the second method the intensity of the scanning spot during writing is constant or modulated at a fixed frequency and the polarity of the magnetic field changes in dependence upon the information. The second method yields a greater information density than the first method and it is possible to overwrite prerecorded information directly with new information. However, it is a problem to realise the required power and the rapid changes of the field at the location of the scanning spot.
A device of the type described above is known from U.S. Pat. No. 3,781,905. In this device the magnetic field is generated by a coil arranged between the objective system and the record carrier. The coil has an air core through which the focused radiation beam passes. A drawback of the known coil is that the core is relatively large so that a large electric power is necessary to generate the required magnetic field. This in turn leads to inadmissable heating of the coil. A further drawback of the known coil is that its height makes it difficult to arrange it in the small space which is available between the objective system and the record carrier.